Required to bring a neutral from a wye transformer?

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greenspark1

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New England
Hi,
I'm in a building (after the service) and have a feeder to a 45kVA step down transformer to go from 600-480V for some equipment. The transformer was already bought as delta-wye. The transformer will connect to a fused disconnect on the secondary side, then out to equipment. None of the loads require the neutral, so I would like to bond the neutral per 250 in the transformer, then take the three phases and a ground out to the disconnect and equipment. Any reason we are required to also bring the neutral? I can't see a safety reason or anything in the Code. Any faults would be cleared by the grounded conductor and overcurrent protection. Thanks for any input!
 
Hi,
I'm in a building (after the service) and have a feeder to a 45kVA step down transformer to go from 600-480V for some equipment. The transformer was already bought as delta-wye. The transformer will connect to a fused disconnect on the secondary side, then out to equipment. None of the loads require the neutral, so I would like to bond the neutral per 250 in the transformer, then take the three phases and a ground out to the disconnect and equipment. Any reason we are required to also bring the neutral? I can't see a safety reason or anything in the Code. Any faults would be cleared by the grounded conductor and overcurrent protection. Thanks for any input!

Off the top of my head I don't see an issue. The "ground" you mention from the xformer to the disconnect is actually a supply side bonding jumper and must be sized per Table 250.66 (2011) or 250.102(C)(1) (2014).
 
Off the top of my head I don't see an issue. The "ground" you mention from the xformer to the disconnect is actually a supply side bonding jumper and must be sized per Table 250.66 (2011) or 250.102(C)(1) (2014).

Good call on the SSBJ, that'll bump it up in size. Thanks. The tricky part is that the feed from the transformer runs to another building, so another ground electrode (ground rod) will be required and tied to the SSBJ at the first disconnecting means(250.32).

A coworker once got bit by not running the neutral from a wye utility transformer. Big cost implication there. But a service is different than feeder.
 
As a point of reference you might look at 250.30.
As I read it I am in agreement that you do not have to ground the neutral, however, I believe that 250.21(B) will require a ground detector.
 
As a point of reference you might look at 250.30.
As I read it I am in agreement that you do not have to ground the neutral, however, I believe that 250.21(B) will require a ground detector.

I think you may have misread the OP. They way understand it it will be a grounded Y secondary. He just does not need the neutral for load purposes. It appears that the OP has a grasp of fault return concepts and requirements.
 
Good call on the SSBJ, that'll bump it up in size. Thanks. The tricky part is that the feed from the transformer runs to another building, so another ground electrode (ground rod) will be required and tied to the SSBJ at the first disconnecting means(250.32).

A coworker once got bit by not running the neutral from a wye utility transformer. Big cost implication there. But a service is different than feeder.

After the xformer secondary disco it becomes a feeder with a EGC sized per 250.122 and you still don't need a neutral. At the outbuilding you need a disconnect with only an equipment ground bar to connect the EGC of the feeder and the GEC at the out building. Sounds like you have the hang of it though.
Just a thought, while not required, you sure you want to do this without a neutral available? It seems like something always comes up at some point where you need that neutral. It sure is hell to add later.:p
 
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I think you may have misread the OP. They way understand it it will be a grounded Y secondary. He just does not need the neutral for load purposes. It appears that the OP has a grasp of fault return concepts and requirements.
Thank you. I'm sure the long time posters here realize that with age my mind is reading what it wants to even more so (kinda scary on this end). My apologies and my appreciation for watching after me :) God may be telling me my posting days are numbered.
 
Thank you. I'm sure the long time posters here realize that with age my mind is reading what it wants to even more so (kinda scary on this end). My apologies and my appreciation for watching after me :) God may be telling me my posting days are numbered.

Oh augie, you still have lots of posting left in you. Your kind words and wisdom are appreciated by all.:)
 
After the xformer secondary disco it becomes a feeder with a EGC sized per 250.122 and you still don't need a neutral. At the outbuilding you need a disconnect with only an equipment ground bar to connect the EGC of the feeder and the GEC at the out building. Sounds like you have the hang of it though.
Just a thought, while not required, you sure you want to do this without a neutral available? It seems like something always comes up at some point where you need that neutral. It sure is hell to add later.:p

The cost of adding a neutral to the feeder will probably be a very small percentage of the cost of this project. Adding a neutral later will be much more expensive. Unless there is a lot of pressure to keep the cost down, you may want to consider at least bringing the neutral to the outbuilding disconnect. That way you won't be taking the neutral to equipment that doesn't need it, but it is still available in the outbuilding for the next project that comes along and requires it.
 
The cost of adding a neutral to the feeder will probably be a very small percentage of the cost of this project. Adding a neutral later will be much more expensive. Unless there is a lot of pressure to keep the cost down, you may want to consider at least bringing the neutral to the outbuilding disconnect. That way you won't be taking the neutral to equipment that doesn't need it, but it is still available in the outbuilding for the next project that comes along and requires it.

Good idea to keep the neutral and run it to the first disconnect just in case. I'll run it by the building folks and see what they think. Thanks all!
 
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